1. Field of Invention
The present invention relates to the technical field of an electro-optical device of an active matrix drive system, and more particularly, to the technical filed of an electro-optical device of a type having pixel switching thin film transistors (hereinafter, referred to as TFTs) disposed in a laminated layer structure on a substrate.
2. Description of Related Art
In electro-optical devices of a TFT active matrix drive system, when incident light beams are irradiated on the channel region of a pixel switching TFT associated with each pixel, a current is generated thereto by the excitation caused by the light beams so that the characteristics of the TFT are changed. In particular, in electro-optical devices used for light bulbs of projectors, since incident light beams have high intensity, it is important to shade light beams incident on the channel region and its peripheral region of a TFT. Thus, the channel region and its peripheral region are conventionally shaded by a shading film disposed at a confronting substrate to prescribe the opening region of each pixel or by a data line passing on the TFT and formed of a metal film of Al or the like. Japanese Unexamined Patent Application Publication No. 9-33944 discloses a technology for reducing light beams incident on a channel region by a shading film formed of a-Si (amorphous silicon) having a large refractive index. Further, a shading film formed of, for example, a metal having a high melting point, is sometimes disposed on a TFT array substrate at a position facing a pixel switching TFT (that is, below the TFT). The shading film also disposed below the TFT can prevent light beams reflected on the back surface of the TFT array substrate from being incident on the TFT of the electro-optical device as well as can prevent projected light beams, which have passed through a prism and the like when one optical system is constructed by a combination of a plurality of electro-optical devices through the prism and the like, from being incident on the TFT of the electro-optical device.
However, the above-mentioned various types of the shading technologies have the following problems. That is, first, according to the technology for forming the shading film on the confronting substrate and on the TFT array substrate, the shading film is considerably separated from the channel region through, for example, a liquid crystal layer, electrodes, an interlayer insulation film when observed three-dimensionally, and light beams incident obliquely between the shading film and the channel region cannot be sufficiently shaded. In particular, in small electro-optical devices used as light bulbs of projectors, light beams incident thereon are obtained by stopping light beams projected from a light source through a lens and that contain an obliquely incident light component in an amount which cannot be disregarded. Thus, it is a problem in practical use that such obliquely incident light beams are not sufficiently shaded.
In addition to the above problems, after light beams, which have traveled into an electro-optical device from a region having no shading film, and are reflected by a shading film and the inner surface of a data line (that is, the surface thereof facing a channel region), the reflected light beams, or light beams, which are created when the reflected light beams are further reflected by the shading film and the inner surface of the data line a plurality of times (hereinafter, referred to as xe2x80x9cmultipath-reflected light beamsxe2x80x9d), may finally reach the channel region of a TFT. Further, according to the technology for shading light beams by a data line, it is basically difficult for the data line to sufficiently shade light beams, because the data line is formed in a striped shape which extends perpendicularly to a scanning line when observed on a plan view. It is also necessary to dispose a thick interlayer insulation film therebetween in such a degree that the adverse affect of the capacitance coupling between the data line and the channel region can be disregarded.
Further, according to the technology described in Japanese Unexamined Patent Application Publication No. 9-33944, a relatively thick interlayer insulation film must be laminated between a gate electrode and an a-Si film to reduce the adverse affect of the capacitance coupling therebetween to form an a-Si film on a gate line. As a result, the additional formation of the a-Si film, the interlayer insulation film, and the like makes a laminated structure complex and increases its size. It is also difficult to sufficiently shade obliquely incident light beams and inner-surface reflected light beams. In particular, since electro-optical devices are miniaturized and the pixel pitches thereof are greatly narrowed to cope with a recent requirement for enhancing the quality of a displayed image, it is more difficult to sufficiently shade light beams by the various types of the above-mentioned conventional technologies. Accordingly, a problem arises in that the quality of a displayed image is lowered by flickering of the image and the like caused by the change of the characteristics of TFTs.
It should be noted that, while it is contemplated to increase a region where a shading film is formed to increase the light resistant property, an increase in the region where the shading film is formed causes a problem in that it is fundamentally difficult to increase the opening ratio of each pixel in order to enhance the brightness of a displayed image.
It is therefore an object of the present invention, which was made in view of the above-mentioned problems, to provide an electro-optical device which is excellent in its light resistant property, and which has a relatively large opening ratio of each pixel and can display an image of high quality.
To solve the above problems, an electro-optical device of the present invention includes a pair of substrates, an electro-optical substance interposed between the pair of substrates, pixel electrodes formed on one of the pair of substrates, thin film transistors connected to the pixel electrodes, a shading layer that covers at least the channel regions of the thin film transistors, and a light absorption layer interposed between the shading layer and the thin film transistors.
According to the electro-optical device of the present invention, at least the channel regions of the thin film transistors connected to the pixel electrodes are shaded by the shading layer.
When a shading layer formed of a metal film having a shading property such as an Al (aluminum) film, a Cr (chromium) film, or the like is generally used, light beams incident on the thin film transistors from a side where the shading layer is disposed basically can be sufficiently shaded by reflecting the light beams by the surface, which does not face the thin film transistors, of the shading layer (that is, by the outer surface of the shading layer in the electro-optical device). More specifically, when the shading layer is disposed on a side where light beams (for example, projected light beams when the electro-optical device is applied to a projector) are incident on the thin film transistors, the incident light beams can be shaded by the outer surface of the shading layer. Otherwise, when the shading layer is disposed on a side from which incident light beams emerge with respect to the thin film transistors, return light beams (for example, light beams reflected on a back surface when the electro-optical device is applied to the projector, light beams passing through a composite optical system from other light bulb when a plurality of electro-optical devices are used in combination as a light bulb as in a case in which the electro-optical devices are applied to a double-panel type projector) can be shaded by the outer surface of the shading layer. However, return light beams, which pass aside the thin film transistors from an opposite side of the shading layer and are oblique to the substrate (for example, when the shading layer is disposed to the side of the thin film transistors on which light beams are incident) or incident light beams (for example, when the shading layer is disposed to the side of the thin film transistors from which light beams emerge) are at least partly reflected by the front surface, which faces the thin film transistors, of the shading layer (that is, the inner surface of the shading layer in the electro-optical device). Thus, inner-surface-reflected light beams are generated between the shading layer and the thin film transistors by these oblique incident light beams and return light beams reflected on the inner surface of the shading layer. Further, multiple reflection is also caused when the inner-surface-reflected light beams are reflected by another film. Accordingly, even if the shading layer is simply disposed at the thin film transistors, inner-surface-reflected light beams and multipath-reflected light beams are caused by light beams reflected by the inner surface of the shading layer and finally incident on the thin film transistors, regardless of the size of the shading layer and the location where the shading layer is disposed. As a result, the characteristics of the thin film transistors are deteriorated by these internally-reflected light beams and multipath-reflected light beams.
According to the present invention, however, light beams, which pass aside the thin film transistors from the opposite side of the shading layer and tend to obliquely reach the inner surface of the shading layer, and light beams, which are reflected by the inner surface of the shading layer, are absorbed by the light absorption layer interposed between the shading layer and the thin film transistors. As a result, when the shading layer formed of the metal film having a high reflectance, such as the Al film, the Cr film is disposed and sufficiently shades light beams incident on the outer surface of the shading layer, the transistor characteristics can be effectively prevented from being deteriorated by light leakage. Further, reduction of a contrast ratio caused by light beams passing through an image display region can be effectively prevented by the shading layer. On the other hand, since the inner-surface-reflected light beams and the multipath-reflected light beams are absorbed by the light absorption layer, the deterioration of the transistor characteristics caused by the light leakage can be more effectively reduced or prevented. Moreover, light beams can be shaded and absorbed at a location relatively near to the thin film transistors as compared with a case in which they are shaded and absorbed by, for example, a shading layer disposed to a conventional confronting substrate, which can enhance a shading performance while avoiding an unnecessarily increase in a region where the shading layer is formed (that is, without unnecessarily reducing the non-opening region of each pixel).
As a result, an electro-optical device can be realized in which respective pixels have a high opening ratio. Also, deterioration of the characteristics of thin film transistors due to light leakage can be reduced by a high light resistant property. An electron optical device can be provided, which has a high contrast ratio, and which can display an image of high quality.
It should be noted that the interlayer distance between the shading layer and the light absorption layer in the present invention may be small by interposing no film or a very thin insulation film, or the like therebetween, or may be large by interposing a somewhat thick interlayer insulation film therebetween. As described below, however, it is advantageous to reduce the interlayer distance between the shading layer and the light absorption layer from a view point of constructing a storage capacitor by using the shading layer and the light absorption layer as a pair of capacitance electrodes, and from a view point of enabling heat generated by the light absorption layer to escape, through the shading layer.
In one aspect of the electro-optical device of the present invention, the light absorption layer is mainly formed of a material which mainly forms the channel regions of the thin film transistors. The light absorption layer is formed of a polysilicon film mainly formed of, for example, silicon and containing P, B, or As doped thereto to make the silicon conductive.
Further, the channels of the thin film transistors are formed of polysilicon mainly including silicon. The polysilicon is doped with a slight amount of B, P, As or the like to control the threshold voltage Vth of the thin film transistors, or is not doped with any material.
Further, amorphous silicon or single crystal silicon may be used for the channels and the light absorption layer in place of the polysilicon.
In another aspect of the electro-optical device of the present invention, the light absorption layer is formed of a silicon film.
According to this aspect, light beams, which tend to reach the inner surface of the shading layer, and light beams, which are reflected by the inner surface, can be absorbed by the light absorption layer formed of the silicon film. Therefore, the occurrence of the inner-surface-reflected light beams and the multipath-reflected light beams can be effectively reduced or prevented. In particular, when the polysilicon film is employed as a semiconductor layer serving as the channel regions of the thin film transistors, the light absorption layer has a light absorbing property that is similar to, or the same as, the light absorbing property (frequency depending property and the like) in the channel regions. Accordingly, the light absorption layer formed of the silicon film is very advantageous because light beams including a light component, which becomes a cause of light leakage when absorbed by the channel regions, can be absorbed and removed by the light absorption layer.
In another aspect of the electro-optical device of the present invention, the shading layer is formed of a film containing metal.
According to this aspect, incident light beams and return light beams can be sufficiently shaded by the shading layer formed of the film containing metal. At this time, since internally-reflected light beams and multipath-reflected light beams can be particularly absorbed and removed by the light absorption layer, a film containing metal having a very high reflectance, such as an Al film, and the like, can be employed. It should be noted that exemplified as the film containing metal, in addition to the Al film, is a film formed of single metal, alloy, metal silicide, polysilicide, a laminated film thereof, and the like, containing at least one of high melting point metals, for example, Ti (titanium), Cr (chromium), W (tungsten), Ta (tantalum), Mo (molybdenum), Pb (lead), and the like.
In another aspect of the electro-optical device of the present invention, the shading layer is disposed above the thin film transistors on the substrate.
According to this aspect, incident light beams can be shaded by the outer surface of the shading layer disposed above the thin film transistors. Then, since return light beams, which tend to reach the inner surface of the shading layer, and light beams, which are reflected by the inner surface thereof, are absorbed and removed by the light absorption layer, the deterioration of the characteristics of the thin film transistors due to the internally-reflected light beams and the multipath-reflected light beams resulting from the reflection of light beams on the inner surface of the shading layer can be reduced or prevented by the shading layer and the light absorption layer.
In the aspect in which the shading layer is disposed on the upper side, the shading layer may be formed of data lines.
With this arrangement, when data lines composed of an Al film, or the like, are provided with a function as a shading layer in addition to a function as wiring, it is possible to prevent a laminated structure from becoming complex by additionally forming a dedicated shading layer. Accordingly, this arrangement is very advantageous by simply arranging the electro-optical device, and simplifies a manufacturing process thereof.
In the aspect in which the shading layer is disposed on the upper side, the shading layer may be formed of capacitance lines interposed between the data lines and the thin film transistors, and the light absorption layer may be formed of capacitance electrodes disposed in confrontation with the capacitance lines through a dielectric film and separated in an island shape for each pixel.
With this arrangement, the provision of the function as the shading layer with the capacitance lines formed of the metal film, the polysilicon film, or the like, in addition to the function as the wiring, as well as the provision of the function as the light absorption layer with the capacitance electrodes formed of the polysilicon film, or the like, in addition to the function as the electrodes, prevents the laminated structure from becoming complex by additionally forming a dedicated shading layer and a dedicated light absorption layer. Accordingly, this arrangement is very advantageous by simply arranging the electro-optical device, and simplifies a manufacturing process thereof.
In the aspect in which the shading layer is disposed on the upper side, the shading film may be formed of a plurality of data lines connected to the thin film transistors and extending in a first direction, respectively, and a plurality of capacitance lines connected to the pixel electrodes and extending in a second direction intersecting the first direction, respectively.
With this arrangement, the provision of the function as a part of the shading layer with the data lines formed of the Al film, or the like, in addition to the function as the wiring, as well as the provision of the function as a part the shading layer with the capacitance lines formed of the metal film, polysilicon film, or the like, in addition to the function as the wiring, prevents the laminated structure from becoming complex by additionally forming a dedicated shading layer. In particular, when the data lines are used as the shading layer in the direction along the data lines, and the capacitance lines are used as the shading layer in the direction along the capacitance lines or scanning lines, no waste is caused in the layout of wiring. Accordingly, this arrangement is very advantageous by simply arranging the electro-optical device, and simplifies a manufacturing process thereof.
Otherwise, according to this aspect in which the shading layer is disposed on the upper side, the shading layer may be formed of one layer of capacitance lines interposed between data lines and the thin film transistors, and having a multilayer structure, and the light absorption layer may be formed of another layer of the capacitance lines that is located nearer to the thin film transistors than the one layer.
With this arrangement, both a shading function and a light absorbing function can be provided by the capacitance lines, which have the multi-layer structure, including both the shading layer and the light absorption layer. In addition to the above, it is also possible to enable heat generated in the light absorption layer when it absorbs light beams to escape through the shading layer.
Further, in various situations in which the capacitance lines are provided as described above, the capacitance lines may be formed in a striped shape extending in a direction intersecting the data lines in an image display region, and may be connected to a constant potential source located in a peripheral region located in the vicinity of the image display region.
With this arrangement, the capacitance lines can be set to a constant potential in the peripheral region, so that the constant potential portion of the capacitance lines, that is disposed facing the respective capacitance electrodes in the image display region, can suitably function as fixed potential side capacitance electrodes constituting a storage capacitor. Therefore, the performance of the storage capacitor can be enhanced. The constant potential source may be a constant potential source, such as a positive power supply or a negative power supply, which is supplied to a periphery drive circuit to drive the thin film transistors, or a constant potential source supplied to the confronting electrodes of the confronting substrate.
When the capacitance lines are connected to the constant potential source as described above, the capacitance lines may be connected to each other in the peripheral region, and may be connected to the constant potential source as a whole through one or a plurality of contacts.
With this arrangement, in the image display region, the plurality of striped-shaped capacitance lines can be connected to the constant potential as a whole in the peripheral region through the one or plurality of contacts (for example, the contacts disposed at the four corners of the substrate).
Otherwise, when the capacitance lines are connected to the constant potential source as described above, the capacitance lines may be connected to each other in the peripheral region, and may be redundantly connected to the constant potential source as a whole through a plurality of contacts.
With this arrangement, in the image display region, the plurality of striped-shaped capacitance lines can be stably and reliably connected to the constant potential in the peripheral region through the plurality of contacts disposed redundantly.
Further, according to this aspect in which the shading layer is disposed on the upper side as described above, another shading layer may further be provided, which is disposed below the thin film transistors on the substrate, to cover at least the channel regions of the thin film transistors.
With this arrangement, return light beams, traveling from the lower side of the thin film transistors, can be shaded by the other shading film so that the thin film transistors can be shaded from the upper and lower sides thereof. At this time, internally-reflected light beams and multipath-reflected light beams, which particularly tend to be created between the two shading films, can be absorbed and shaded by the light absorption layer. The other shading film may be formed of single metal, alloy, metal silicide, poly-silicide, a laminated film thereof, or the like, containing at least one of high melting point metals, for example, Ti, Cr, W, Ta, Mo, Pb.
In this case, the other light absorption layer may be interposed between the other shading layer and the thin film transistors. The other light absorption layer being mainly formed of a material (for example, silicon or polysilicon) which mainly forms the channel regions of the thin film transistors.
With this arrangement, the internally-reflected light beams and the multipath-reflected light beams, which tend to be created between the two shading films, can more strongly be absorbed and shaded by the two light absorption layers.
In another aspect of the electro-optical device of the present invention, the shading layer is disposed below the thin film transistors on the substrate.
According to this aspect, return light beams can be shaded by the outer surface of the shading layer disposed below the thin film transistors. Then, since incident light beams, which tend to reach the inner surface of the shading layer, and light beams, which are reflected by the inner surface thereof, are absorbed and removed by the light absorption layer, the deterioration of the characteristics of the thin film transistors due to the internally-reflected light beams and the multipath-reflected light beams resulting from the reflection of light beams on the inner surface of the shading layer can be reduced or prevented by the shading layer and the light absorption layer. The shading film disposed below the thin film transistors may be formed of single metal, alloy, metal silicide, poly-silicide, a laminated film thereof, or the like, containing at least one of high melting point metals, for example, Ti, Cr, W, Ta, Mo, Pb.
In another aspect of the electro-optical device of the present invention, the light absorption layer includes a portion that includes an intermediate conductor layer that transits and connects the pixel electrodes or the data lines to the thin film transistors.
According to this aspect, the provision of the function as a part of the light absorption layer with the intermediate conductor layer formed of the polysilicon film, or the like, in addition to the transiting and connecting function, can prevent the laminated structure from becoming complex by additionally forming a dedicated light absorption layer. Accordingly, this arrangement is advantageous by simply arranging the electro-optical device, and simplifies a manufacturing process thereof. It should be noted that when the intermediation and connection are executed by making use of the intermediate conductor layer, the connection between the thin film transistors and the pixel electrodes, and between the thin film transistors and the data lines, can be excellently performed through at least two series contact holes, each having a relatively small diameter, while avoiding a technical difficulty of executing the connection through one contact hole, even if the distance between the thin film transistors and the pixel electrodes, and the distance between the thin film transistors and the data lines, is long.
In another aspect of the electro-optical device of the present invention, the shading layer has a heat conductivity that is higher than that of the light absorption layer.
According to this aspect, it is possible for heat generated in the light absorption layer when it absorbs light beams through the shading layer having the high heat conductivity to escape. That is, the quantity of heat transmitted from the light absorption layer to the thin film transistors can be reduced, whereby heat leakage generated in the thin film transistors can be reduced. As a result, the transistor characteristics can be greatly enhanced by reducing both the light leakage and the heat leakage by the shading film and the light absorption layer.
In this aspect, the interlayer distance between the thin film transistors and the light absorption layer may be larger than that between the light absorption layer and the shading layer.
With this arrangement, it is possible to more effectively escape heat generated in the light absorption layer, when it absorbs light beams through the shading layer disposed in the vicinity of the light absorption layer. That is, the quantity of heat transmitted to the thin film transistors can be reduced by the distance of the light absorption layer disposed farther. An interlayer insulation film or the like is interposed between the thin film transistors and the light absorption layer, and between the light absorption layer and the shading layer.
In another aspect of the electro-optical device of the present invention, the shading layer is laminated on the light absorption layer through an insulation film, and is formed slightly larger than the light absorption layer when observed in plan view.
According to this aspect, light beams incident on the outer surface of the shading layer, which is slightly larger than the light absorption layer, can be shaded by the shading film, and, at the same time, light beams, incident on the inner surface of the shading layer, can be absorbed by the light absorption layer, which is slightly smaller than the shading layer.
In another aspect of the present invention, an electro-optical device includes a pair of substrates, an electro-optical substance interposed between the pair of substrates, a pixel electrodes formed on one of the pair of substrates thin film transistors connected to the pixel electrodes, a first shading layer that covers at least the channel regions of the thin film transistors, and a first light absorption layer facing the first shading layer through the thin film transistors.
According to this aspect, the light beams incident on the thin film transistors are shaded by the first shading layer and absorbed by the first light absorption layer, so that the light beams are prevented from being reflected to the thin film transistors.
Further, it is preferable that the first shading layer be disposed on a light incident side with respect to the thin film transistors.
According to this aspect, the first shading layer can prevent light beams from being directly irradiated to the thin film transistors.
Further, it is preferable that a second light absorption layer be interposed between the first shading layer and the thin film transistors.
According to this aspect, the light beams directed to the thin film transistor side of the first shading layer by internal reflection and the like can be absorbed by the second light absorption layer.
Further, it is preferable that a second shading layer be disposed on a side opposite to the first light absorption layer with respect to the thin film transistors.
According to this aspect, the light beams directed to the thin film transistors by internal reflection and the like can be shaded by the second shading layer.
Further, the second shading layer may be formed in a region inside of the first light absorption layer.
According to this aspect, even if strong light beams are obliquely irradiated to the first light absorption layer extending from the second shading layer and leak from the first light absorption layer, the light beams can escape to the exterior.
Further, the second shading layer is formed in a region inside of the first shading layer.
According to this aspect, the second shading layer can avoid oblique light beams.
In another aspect of the electro-optical device the present invention, the electro-optical device includes a pair of substrates, an electro-optical substance interposed between the pair of substrates, pixel electrodes formed on one of the pair of substrates, thin film transistors connected to the pixel electrodes, a first light absorption layer that covers at least the channel regions of the thin film transistors, and a second light absorption layer facing the first light absorption layer through the thin film transistors.
According to this aspect, obliquely incident light beams in particular can be absorbed by the first and second light absorption layers, which can reduce light beams irradiated to the thin film transistors.
Further, light transmitting insulation films are interposed among the pixel electrodes, the thin film transistors, and the first light absorption layer, respectively.
In an aspect of a projecting type display device of the present invention, the projecting type display device includes a light source, light bulbs, each including an electro-optical device, light conductors that introduce light beams emitted from the light source to the light bulbs, and a projecting optical member that projects light beams modulated by the light bulbs.
According to this aspect, since it is difficult for light beams to enter the thin film transistors in the electro-optical device, an image of high quality can be projected.
In an aspect of a substrate for electro-optical device of the present invention, the substrate includes pixel electrodes, thin film transistors connected to the pixel electrodes, a shading layer that covers at least the channel regions of the thin film transistors, and a light absorption layer interposed between the shading layer and the thin film transistors.
In an aspect of the substrate for electro-optical device of the present invention, the substrate includes pixel electrodes, thin film transistors connected to the pixel electrodes, a first light absorption layer that covers at least the channel regions of the thin film transistors, and a second light absorption layer facing the first light absorption layer through the thin film transistors.
In an aspect of the substrate for electro-optical device of the present invention, the substrate includes pixel electrodes, thin film transistors connected to the pixel electrodes, a first light absorption layer that covers at least the channel regions of the thin film transistors, and a second light absorption layer facing the first light absorption layer through the thin film transistors.
The thin film transistors of the present invention may be of a so-called top gate type in which gate electrodes formed of a part of scanning lines are located above channel regions, or may be of a bottom type in which gate electrodes formed of a part of scanning lines are located below channel regions. Further, the interlayer positions of pixel electrodes may be located above or below scanning lines on a substrate.